1. Field of the Invention
Embodiments relate to methods for handling a telecommunications connection, telecommunications arrangement, a switching device, and a network coupling device, in which the telecommunications connection supports the transmission of frequency-coded signals on a payload channel.
2. Background of the Related Art
A telephone system requires an exchange like a PABX (Private Automatic Branch Exchange) to control performance features, in many cases, like the detection of user input during the call. This is particularly the case when no other data channels are available alongside the voice connection for signaling.
Prior art includes signaling user input in communications systems via DTMF signals. DTMF (Dual Tone Multi-Frequency) is a multi-frequency dialing method for which dialed numbers or buttons on a terminal are represented by combining two pure tones (sinusoidal audio signals). The pure tones are transmitted and interpreted in an exchange or the like. For a type of transmission known as outband transmission, the signals are transmitted in the signaling channel, e.g., in the D channel on ISDN. For a type of transmission known as inband transmission, the signals are transmitted in the voice channel, e.g., as tones. In this classic communications environment, two communication partners are interconnected in what is known as the switching network. By using DTMF receivers, the switching technology can decide when DTMF detection is necessary, and it can connect a suitable code receiver to the existing call via the switching network.
In the evolution to VoIP, it became advantageous to use digital signal processors (DSP). In this case, two VoIP terminals were also interconnected in the switching network. Subsequent evolutionary steps led to “direct payload negotiation” to reduce the use of digital signal processors to the extent possible, and to also allow purely software-based VoIP switching systems. In this case, in the signaling channel, the type of DTMF transmission is negotiated first, e.g., RFC2833, and then special packets are transmitted in the payload channel, e.g., RTP, which represent the DTMF signals. With VoIP solutions, however, the signaling and payload channels are often routed over different paths. This can make it so the voice channel no longer passes through the exchange (PABX). The detection of DTMF signals by the exchange is then no longer possible because only the signaling stream is routed to the PABX, but not the payload stream. Previously, the problem could only be solved by interrupting the direct voice connection to detect DTMF signals, and incorporating digital signal processors again.
Thus, the detection of DTMF signals for an exchange in the VoIP environment is often no longer possible, and performance features can no longer be provided during the call.